32-bit mesa will be available in the Ubuntu 18.04 repository. Note that mesa already gets updates in 18.04 which track the versions from later Ubuntu releases, as part of hardware enablement. If incompatibilities are introduced beyond 20.04 (which is the cutoff for hardware enablement backports for 18.04), we will need to address them on a case-by-case basis.
PCSX2, as the plan stands today, would be available only in the 18.04 repository - so would be available at version 1.4.0. i386-only application packages currently distributed in Ubuntu are strong candidates for being converted to snaps. It looks like there’s been at least one effort already to package PCSX2 as a snap (pcsx2-tabetai).
Can you clarify why you’re interested to know about newer versions of libraries? Because i386 would be treated as “legacy”, it would not get newer library versions. But since the vast majority of i386-only software is also legacy (closed-source, will never be rebuilt), it also does not generally benefit from newer libraries. Do you have something specific in mind?